Tryptophan 7-halogenase (EC 1.14.19.9, PrnA, RebH) is an enzyme with systematic name L-tryptophan:FADH2 oxidoreductase (7-halogenating). This enzyme catalyses the following chemical reaction: tryptophan + FADH2 + Cl− + O2 + H+ 7-chloro-L-tryptophan + FAD + 2 H2O The enzyme can use bromide ions (Br−) in place of chloride (Cl−).